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Alt screen separate scrollback

Category: scrollback · Baseline: core · Tags: Xterm Extensions · Specification ↗

Tests whether the alternate screen buffer maintains its own separate scrollback, independent from the main screen's scrollback. Most terminals do not provide scrollback in the alternate screen — full-screen applications are expected to manage their own scrolling. Some terminals (like Kitty) offer configurable behavior for alternate screen scrollback.

How this is testedautomated
Write "NORMAL", enter alt screen with \x1b[?1049h, verify altScreen mode is active.

The same probe runs against headless backends (via Termless) and real terminal apps (via a daemon launched in each terminal). This lets us distinguish parser correctness from rendering correctness.

Analysis2026-04-06

Supported by 11 of 12 terminals (92%). Not supported by: vt100.js. Part of the Core TUI baseline. Notes: vt100.js: Not in VT100/VT220 — no alternate screen buffer.

Supported by 13 of 14 backends (93%)

Terminal Applications

Terminal	Version	Support	Notes
iTerm2	3.6.9	✓ yes
Ghostty	1.3.1	✓ yes
VS Code		✓ yes
Warp		✓ yes
Cursor		✓ yes
Terminal.app		✓ yes

Headless Backends

Parser correctness only — a ✓ means the parser accepts the sequence.

Backend	Version	Support	Notes
Alacritty	0.26.0	✓ yes
Kitty	0.40.0	✓ yes
vterm	0.2.0	✓ yes
WezTerm	0.1.0-fork.5	✓ yes
xterm.js	5.5.0	✓ yes
vt100.js	0.2.1	✗ no	Not in VT100/VT220 — no alternate screen buffer

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